check the body mounts for signs of stress/or bad rust, the frame in the area around where the gas tank/ spring hangers for rust out, sometimes the valve stem seals can dry out and cause the engine to smoke after they have sat for a long time, with a body lift look for strecthed hoses, wiring etc, also make sure that the shifters work ok with the body lift. if its been wheeled look for cracks at the ends of the radius arms or bent/torn bracketts on the ttb, cracks on the pillars around the rain gutters[ most full size broncos that are wheeled will have them ]the tailgates are very prone to rusting out so much they have to be replaced.